audio – Page 3 – Engineering Radio

What bitrate is needed to sound like analog FM?

As it turns out, 300 kbp/s or greater. At least in critical listening environments according to the paper titled Perceived Audio Quality of Realistic FM and DAB+ Radio Broadcasting Systems (.pdf) published by the Journal of the Audio Engineering Society. This work was done by a group in Sweden that made various observations with different program material and listening subjects. Each person was given a sample of analog FM audio to listen to, then they listened to various audio selections which were using bit reduction algorithms (AKA CODEC or Compression) and graded each one. The methodology is very thorough and there is little left for subjective interpretation.

In less critical listening environments, bit rates of 160-192 kbp/s will work.

I made a chart and added HD Radio’s proprietary CODEC HDC, which is similar to, but not compatible with AAC:

System	Codec	Bit Rate (kbp/s)
HD Radio FM; HD1 channel*	HDC (similar to AAC)	96 – 144
HD Radio FM; HD2 channel*	HDC	24-48
HD Radio FM; HD3 channel*	HDC	24-48
HD Radio AM*	HDC	20-60
DRM30 (MF-HF)	AAC/HE-AAC	34-72
DRM+ (VHF)	AAC/HE-AAC	700
DAB+	AAC/HE-AAC	32 – 128
DAB	MPEG II, Dolby Digital	192 – 256
Blu-ray	PCM**	≥6 Mbp/s
DVD	PCM, DTS, Dolby Digital	>800
CD-A	PCM	1,411
Web Streaming	MPEG I,II,III, WMA, AAC, etc	32-320, 128 typical
iTunes	AAC	128 – 256
Spotify	Ogg Vorbis	96 – 320
Wimp	AAC/HE-AAC	64 – 256

*Hybrid mode
**PCM: uncompressed data

This is the composite Mean Basic Audio Quality and 95% confidence intervals for the system across all excerpts:

Over the years, we have simply become accustomed to and now accept low-quality audio from mp3 files being played over cheap computer speakers or through cheap ear buds. Does this make it right? In our drive to take something good and make it better, perhaps it should be, you know: Better.

Special thanks to Trevor from Surrey Electronics Limited.

New Studio Project, Part II

The finished product:

This is the finished product from an earlier post. Currently, it is the studio for WAJZ in Albany, but that is not permanent. The SAS studio goes together fairly quickly, as most of the trunking between the TOC and studio is done over the SAS data channel.

The studio monitors (Tanoy Reveal) are set on little posts under the computer screens. I like this setup as the DJs are less likely to rock the house if they decide to crank up the volume on their favorite tune. I am also kind of digging the lack of a tabletop equipment pod. That takes up a lot of countertop space and always seems to be in the way. There are two CD players racks mounted below the counter (lower left), which are almost never used.

WDST, Woodstock, New York

WDST is a well-known radio station in Woodstock, NY. Formatically, I would call it Adult Album Alternative (AAA) and it is one of my favorite stations to listen to. We also do the engineering work for this station. While I was there last week, I snapped a few pictures of the studios:

All of the studio use Audioarts R-60 consoles, which are in good condition considering their age. Lots of guest microphones and the windows look out into a performance venue.

WDST music library, located in hallway outside of studio — WDST music library, located in the hallway outside of the studio

The music library is extensive.

The production room, another R-60 console. I don’t know where the microphone disappeared to, perhaps it was borrowed by the morning show.

Technical Operation Center (TOC). WDST uses NextGen from RCS for music storage, playback and automation. Other equipment includes ISDN, POTS phone, Distribution Amps, Limiters, streaming computer, STL, etc.

WDST transmitter, Broadcast Electronics FM5C

The transmitter site is on Hallihan hill, across the street from the old ATT long lines site. The station uses a Broadcast Electronics FM5C transmitter.

Forward power, almost five whole kilowatts of flame throwing power.

WDST antenna, Hallihan Hill, Kingston, NY

The antenna is a Shively 6810 2-bay half wave spaced.

New Studio project

It is time, once again, to replace some very old Pacific Recorders BMXII consoles. The Pacific Recorders consoles were very expensive when new, but after 30 years of continuous use, have more than paid for themselves. The replacement console of choice for this installation is a SAS Rubicon. I have installed these units elsewhere and they are the modern equivalent of the PRE BMX.

The heart of the Rubicon system is the 32KD router. Routed audio systems can save a lot of time and effort in a large studio facility installation. Not having to run and terminate multiple analog and digital trunk cables between the rack room and the studio is a huge deal in a six or ten-studio installation project.

The SAS 32KD router and Rubicon console system use a serial TDM bus to communicate and transport audio around. This is a simpler system than packet-switched IP data. Basically, the console surface is a very large, fancy computer control interface. Here are some pictures of the start of the project:

This is the view from the entry door. The furniture was placed last week and the countertop was cut in for the console. The furniture is made by Studio Technology. The pile of yet-to-be-installed equipment:

For monitors, we are using the Tanoy 602p near field monitor placed on the table top above the computer screens. This studio will not have a turret. Turrets used to be necessary to hold things like cart machines and CD players. These days the CD players are used so infrequently that it was decided to put them in the side rack under the counter top. Turrets also take up a lot of counter top space that can be put to better use.

Punch blocks and power connections. The red outlets are isolated ground UPS type, the back outlets are feed by the emergency generator power panel. All electric wiring is inside of the metal conduit. The punch blocks are the inputs to the SAS RIO link unit, one 16-pair analog audio cable and ten category 5e shielded cables. The cat 5e is used for computer and TDM data buss to the router.

The SAS Rubicon console is cut into the counter top and protected by plastic sheets.

Rack room with 32KD routers. This facility has 9 studios total plus a news room with three work areas.

The SAS 32KD router. All audio from the automation systems, satellite feeds and other sources is connected directly to these units. This unit is on line for other studios that have already been converted to the SAS gear.